Our group is fighting a horde + dozen of level B + 4 level A monsters counting with the fairy.
B Rank: This rank of monster is currently unbeatable with humanity's current level of technology even with using tanks, helicopters, or fighter jets. HERO sends Level 3s to combat this rank.
A Rank: This rank of monster has been denoted as a threat to an entire sector and if left unchecked, countless humans, hundreds of thousands more, will die. There is nothing any human can do against this rank of monster. No amount of preparation they could arrange. Even anti-monster weaponry HERO is developing would be useless against them. Only Level 4s and 5s are used by HERO to combat this rank of monster